Pressure-dependent rheology of bentonite-conditioned sand and its application in EPB shield tunnelling

Earth Pressure Balance (EPB) shield tunneling in water-rich, cohesionless sandy ground faces significant challenges, including tunnel face instability and spewing from the screw conveyor. Conditioning the excavated material with bentonite slurry is a critical technique for ensuring construction safety. However, a comprehensive understanding of the rheological properties of conditioned soil under realistic confining pressures remains elusive, which limits the precise control of tunneling parameters. This study aims to systematically investigate the influence of soil gradation, slurry injection ratio (SIR), and confining pressure ( P ) on the rheology of bentonite-conditioned sand. A custom-developed mechanical pressurized vane rheometer was used to conduct tests on two typical sands—poorly graded sand (SP) and well-graded sand (SW)—under various SIR (25 %–40 %) and confining pressures ( P = 200 kPa, 300 kPa). The results indicate that the conditioned soil behaves as a Bingham fluid, with its yield stress ( τ 0 ) and plastic viscosity ( k ) exhibiting a significant non-linear increase as confining pressure increases and SIR decreases. Based on these laboratory findings, a pressure-dependent rheological parameter dataset was established and integrated into a full-scale three-dimensional computational fluid dynamics (CFD) model. The CFD model, validated against field data from the Shenyang Metro project, accurately predicted the muck pressure distribution and operational parameters within the shield machine, with a maximum relative error of less than 7 %. The findings of this research provide a valuable reference for optimizing soil conditioning strategies and advancing numerical simulations of EPB shield tunneling in similar geological conditions. • Bentonite-conditioned sand exhibits pressure-dependent Bingham fluid properties. • A custom pressurized rheometer quantified the key impact of confining pressure on rheological parameters. • A full-scale CFD model based on laboratory data accurately predicted field performance. • A lab-to-field optimization workflow for EPB shield performance is proposed.